Crystalline silicon (including multi- and mono-crystalline silicon) is the most dominant absorber material for commercial solar photovoltaic (PV) applications, currently accounting for well over 80% of the solar PV market. There are different known methods of forming monocrystalline silicon film and releasing or transferring the grown semiconductor (e.g., monocrystalline silicon) layer. Regardless of the methods, a low cost epitaxial silicon deposition process accompanied by a high-volume, production-worthy low cost method of release layer formation are prerequisites for wider use of silicon solar cells.
Porous silicon (PS) formation is a fairly new field with an expanding application landscape. Porous silicon is created by the electrochemical etching of silicon wafers with appropriate doping in an electrolyte bath. The electrolyte for porous silicon is, for example: HF (49% in H2O typically), isopropyl alcohol (IPA) (and/or acetic acid), and deionized water (DI H2O). IPA (and/or acetic acid) serves as a surfactant and assists in the uniform creation of PS. Additional additives such as certain salts may be used to enhance the electrical conductivity of the electrolyte, thus reducing its heating and power consumption through ohmic losses.
Porous silicon has been used as a sacrificial layer in MEMS and related applications where there is a much higher tolerance for cost per unit area of the wafer and resulting product than solar PV. Typically porous silicon is produced on simpler and smaller single-wafer electrochemical process chambers with relatively low throughputs on smaller wafer footprints. Currently there is no commercially available porous silicon equipment that allows for a high throughput, cost effective porous silicon manufacturing. The viability of this technology in solar PV applications hinges on the ability to industrialize the process to large scale (at much lower cost), requiring development of very low cost-of-ownership, high-productivity porous silicon manufacturing equipment.